Rhea (Moon) Facts Click to share on Reddit (Opens in new window) Similar Facts Iapetus Moon Facts Iapetus is an oddly-colored and shaped moon of Saturn. It is the third-largest moon in the system, and was discovered in 1671 by the... The Width of Saturn’s Rings The rings of Saturn are composed of billions of icy particles ranging in size from tiny grains to kilometres across. There are 14 major divisions in... Titan Moon Facts Titan is the Saturn’s largest moon and is the second largest moon in our solar system. If it were not orbiting Saturn, Titan could be considered... Top Facts Rhea: Saturn's Dirty Snowball Moon Rhea: Saturn's Dirty Snowball Moon By Nola Taylor Redd, Space.com Contributor | June 29, 2016 08:08pm ET MORE This raw image of Saturn's icy moon Rhea was taken on March 10, 2013 by NASA's Cassini spacecraft, and received on Earth March 10, 2013. The camera was pointing toward Rhea at approximately 174,181 miles (280,317 kilometers) away.

Credit: NASA/JPL/Space Science Institute Rhea, the second largest moon of Saturn, is a dirty snowball of rock and ice. The only moon with an oxygen atmosphere, thin though it may be, Rhea is one of the most heavily cratered satellites in the solar system. Discovery and naming Rhea is one of the four moons discovered by Italian astronomer Giovanni Cassini . He spotted the icy moon on Dec. 23, 1672. It was the second moon he observed, and the third to be found in orbit around the ringed planet. At 949 miles (1,528 kilometers) in diameter, it is the second largest moon of Saturn , but less than a third the size of the largest contender, Titan . Cassini named the four moons he discovered the Sidera Lodoicea — the Stars of Louis — after King Louis IV. The moon was first referred to numerically as Saturn V, based on its distance from the planet.

It was not formally named until 1847, when John Herschel (son of astronomer William Herschel ) suggested that the satellites of Saturn be named for the Titans, the brothers and sisters of the Greek god Cronus (known to the Romans as Saturn). Rhea, the daughter of Uranus and Gaea, was the wife of Cronus. Known as the mother of the gods, she gave birth to several of the Olympian gods and goddesses, including Zeus and Hera. She was also mother to Hestia, Hades, Demeter, and Poseidon. The features on the moon are named for people and places from various creation myths. [ Photo Gallery: Icy Rhea: Photos of Saturn's Second-Largest Moon ] On the surface Rhea is an icy body with a density 1.233 times that of liquid water, which implies that it is three-quarters ice and one-quarter rock. The highly reflective surface provides further evidence. When NASA's Cassini-Huygens spacecraft examined Rhea, measurements based on its angular motion led scientists to conclude the moon lacked an icy core. Instead, it resembles a frozen dirty snowball, with ice and rock mixed together.

Temperatures on Rhea range from minus 174 degrees C (minus 281 degrees F) in the warmer, sunlit areas to minus 220 C (minus 364 F) in the shade. At these frigid temperatures, the ice on the moon behaves like rock. Rhea is one of the most heavily cratered satellites in the solar system. Regions on the moon are classified based on their cratering. Heavily cratered, brighter terrain contains impacts larger than 25 miles (40 km), while more lightly cratered regions near the poles and equatorial regions have smaller impacts. Rhea is more heavily cratered than Saturn's other icy moons, Dione and Tethys. It also orbits farther from the planet, averaging 327,490 miles (527,040 km) away. As a result, Saturn's gravitational tug has less of an effect on the moon. Dione and Tethys both show signs of smooth plains, which may have been created when the internal warmth caused by Saturn's gravity melted and re-iced cratered regions. Another explanation is that the distant moon could simply have received more impacts.

The March 2010 Rhea flyby trajectory and oxygen atmosphere distribution (as simulated by computer models). Inset: Predicted oxygen density (yellow), compared to Cassini's measurements (white) taken during the flyby. Credit: Science/AAAS Rhea also contains wispy lines, running tens to hundreds of kilometers across the planet. The Cassini craft revealed that these wisps were fractures in the surface that created canyons, some of which reached several hundred meters in height. As dark material falls from the walls, bright icy material beneath is revealed. Dione and Tethys also house similar wisps. [ Photo Gallery: Icy Rhea: Photos of Saturn's Second-Largest Moon ] A thin atmosphere and rings that weren't A very faint oxygen atmosphere exists around Rhea, the first direct evidence of an oxygen atmosphere on a body other than Earth. The atmosphere is thin, with oxygen measuring about 5 trillion times less dense than that found on Earth. Oxygen could be released as the surface is irradiated by ions from Saturn's magnetosphere. The source of the carbon dioxide is less clear, but could be the result of similar irradiation, or from dry ice much like comets.

At one point, scientists announced the possibility of three narrow bands filled with material ranging in size from pebbles to boulders. The original detection came from plasma measurements taken by Cassini, but later optical observations revealed no rings. The source of the plasma measurements remains a mystery. From maps and data Cassini obtained, scientists are trying to figure out how old features on the surface are, as well as the nature of these features. A 2014 study in the journal Icarus showed that Rhea's Inktomi crater and the blanket of debris surrounding it have more thermal inertia (resistance to being the same temperature as the surroundings) than other areas of the moon. A separate presentation at the American Astronomical Society in 2016 suggests that Rhea (as well as several other moons) would have pelted from the debris of a generation of older moons, in its distant past. A 2015 study in Icarus looked at the relative amounts of crystalline and amorphous (less distinct) water ice, which is useful for worlds that are predominantly icy.

The team studied two craters, Inktomi and Oblata, and found that most of the crystalline ice was in the center of these craters, which was expected because that's where the small body impacted the surface and caused the most disruption. Over time, crystalline ice is exposed to charged particles and it becomes less pristine. Using a known rate of ice transformation, the team estimated the Oblata crater was about 450 million years old.

More facts about Rhea Diameter: 949 miles (1,528 km) Equatorial circumference: 2,057,770 miles (3,311,665 km) Surface area: 2,834,260 square miles (7,340,701 square miles) Mass: 2.306 x 1021 kilograms Density: 1.233 grams per cubic centimeter Average orbit around Saturn: 327,505 miles (527,068 km) Closest approach: 327,177 miles (526,541 km) Farthest approach: 327,832 (527,595 km) Orbit eccentricity: 0.001 Iapetus Iapetus ) is the seventeenth of Saturn 's known satellites and the third largest: orbit : 3,561,300 km from Saturn diameter : 1460 km mass : 1.88e21 kg In Greek mythology Iapetus was a Titan, the son of Uranus, the father

 of Prometheus and Atlas and an ancestor of the human race.

Discovered by Cassini in 1671. With a density of only 1.1, Iapetus must be composed almost entirely of water ice. Trailing side of Iapetus from Voyager 2 The leading and trailing hemispheres of Iapetus are radically different. The albedo of most of the leading hemisphere is about .04, as dark as lampblack, whereas the trailing hemisphere's albedo is .6, as bright as Europa . This difference is so striking that Cassini noted that he could see Iapetus only on one side of Saturn and not on the other. One explanation of this is that the leading hemisphere is dusted with a coating of material knocked off of Phoebe or some other Saturnian body. However, the color of the leading half of Iapetus and that of Phoebe don't quite match. Another possibility is that some active process within Iapetus is responsible. The puzzle is compounded by the fact that the dividing line between the two sides is inexplicably sharp. Near the edge of the dark overlaying material On the last day of 2004, Cassini made its first close encounter with Iapetus.

The images show that the dark material overlays the topography, indicating that it is relatively young. And as in the image to the left, along the edge of the dark area there are many craters where only one side is covered by the dark material; the boundary between the two regions isn't so sharp after all. So far the Cassini's data do not resolve the puzzle of the origin of the dark material but there's more to come! Iapetus's giant equatorial ridge Cassini's first encounter with Iapetus also revealed another striking feature not seen before: a ridge 13 kilometers higher than the surrounding terrain that extends at least 1300 km almost almost exactly parallel with Iapetus's equator (click the image at right for more). All of Saturn 's moons except for Iapetus and Phoebe are very nearly in the plane of Saturn's equator. Iapetus is inclined almost 15 degrees. More about Iapetus Why are the two hemispheres so different? Where did that dark stuff come from? Why is Iapetus' orbit not in the plane of the other moons?

Iapetus, moon of Saturn - The Solar System on Sea and Sky Cassini close-up view of the dark colored side of Iapetus (NASA/JPL/Space Science Institute) Son of Uranus Iapetus [eye-AP-i-tus] is the seventeenth of Saturn's moons and the third largest. It was named after a Greek Titan who was the son of Uranus and the father of Prometheus and Atlas. He was also an ancestor of the human race. According to legend, Iapetus was later imprisoned by Zeus in Tartarus after the rebellion of the Titans against the gods. Iapetus was discovered by Giovanni Cassini in 1671. Most of what we now know this moon came from the Voyager missions. Cassini close-up showing bright terrain coated with dark material (NASA/JPL/Space Science Institute) Cassini image with dark material splattered on light terrain (NASA/JPL/Space Science Institute) A Moon of Contrast Iapetus is probably the most unusual of Saturn's moons. It has a low density similar to that of Rhea. This indicates that it contains very little rocky material and is composed mainly of water ice. Iapetus is a moon of stark contrasts.

Its leading hemisphere is very dark with a slight reddish color, while its trailing hemisphere is very bright. The dark area is one of the darkest terrains in the Solar System, and is darker than asphalt. The reason for this dark matter on the leading side is not known. It could be composed of dark matter swept up from space, or it could be something that flowed out from within the moon. Some astronomers believe that the dark matter could have originated on Saturn's moon, Phoebe. Phoebe has a low albedo. Material could have been blasted into space by impacts, where it was then deposited on the surface of Iapetus. One problem with this theory, however, is that the color of the material on Phoebe and Iapetus do not match. Another theory states that this dark material may have been formed by eruptions of methane from deep within the moon. The fact that this area is fairly devoid of craters would suggest that this material is replenished regularly. One puzzling aspect of this phenomenon is that the dividing line between the dark and light areas is extremely sharp. No one seems to know why. Cassini spacecraft close-up image of Iapetus showing its diverse surface features.

The light areas are likely composed of ice. The darker areas represent a thin coating of an unknown material. (ESA/NASA/JPL/University of Arizona) Features of Iapetus The dark, smooth region of Iapetus is known as the Cassini Regio. Very few craters can be found in this region. Astronomers believe that the dark material that covers this region is continually being replenished, thus covering any new craters that may appear. On the opposite side of Iapetus lies the Roncevaux Terra. This region is littered with hundreds of craters. The largest of these craters is known as Roland and is 90 miles (144 km) in diameter. The second largest crater in this area, called Marsilion, is 84 miles (136 km) in diameter. Iapetus has no detectable atmosphere and no magnetic field. General Astronomy/Planetary Moons - Wikibooks, open books for an open world General Astronomy/Planetary Moons Earth[ edit ] Earth has one moon, usually called "the Moon" and sometimes called Luna. It is the fifth largest moon in the solar system.

Of all the moons of the eight planets, Earth's moon is by far the largest relative to its planet, with a diameter of 3476 km and hence a ratio to Earth's diameter of 0.2764. By comparison, the next largest moon relative to a major planet (Triton of Neptune) has a diameter ratio of just .0546. The Moon's diameter is over 50% greater than that of the dwarf planet Pluto. Mars[ edit ] Mars has two very small moons, both discovered by Asaph Hall. Deimos was discovered Deimos on August 12, 1877. Deimos, the outermost moon, was named for the Greek god of panic. Deimos has a diameter of just 16 km. The inner moon Phobos has a diameter of 26 km and is heavily cratered. Phobos was discovered on August 18, 1877. Phobos was named for the Greek god of fear. Deimos and has far fewer craters then Phobos and the craters are also much smaller.

Jupiter[ edit ] Jupiter currently has 64 discovered satellites and 1 not identified object- like- satellite, but the four Galilean moons (Ganymede, Callisto, Io, and Europa) are by far the largest (in that order). Ganymede[ edit ] Ganymede is the largest planetary satellite in the solar system. With a diameter of 5268 km, it is about 8% larger than the planet Mercury. It is also the only moon in the Solar System with its own magnetosphere. Ganymede was discovered on January 7, 1610 by Galileo Galilei, along with Io, Europa, and Callisto. Callisto[ edit ] Callisto is the second largest Jovian moon (that is, moon of Jupiter), and third in the Solar System (with a diameter of 4820 km). It is 98% of the size of Mercury. Callisto has the oldest surface in the Solar System (this means is the most heavily cratered body in the Solar System) even older than Mercury's. Callisto was discovered in 1610, along with Io, Europa, and Ganymede.

Io[ edit ] Io (pronounced EYE-oh) is the third largest Jovian moon and the fourth largest moon in the solar system. It is slightly bigger than Earth's moon, with a diameter of 3642 km. Discovery/History[ edit ] Wikimedia Commons True Color Image Io has had a long history since its discovery in 1610 by Galileo Galilei. Telescope technology limited observations of Io until the late 1800s when large scale features were able to be resolved on its surface. Observations show that Io has areas of red, brown, orange, and yellow which were later attributed to the abundance of sulfur and sodium on the surface and the unusually high amount of volcanic activity. Io is the most volcanically active body in the solar system. Its activity is due to a great deal of tidal heating from Jupiter and a resonant orbit with Jupiter’s other moons. Origin of Internal Energy[ edit ] Io has a similar density to our moon, but is made mostly of sulfur compounds [1] . Io experiences a large amount of tidal heating because it orbits Jupiter at a relatively close distance of 422,000 km and gravitational interactions with other Galilean moons .

Jupiter’s large gravitational field and Io’s interactions with other satellites have resulted in an orbital resonance between Io, Europa , and Ganymede which means their orbital periods are integer multiples of each other [2] . Wikimedia Commons Io Eruption Plume Image For each orbit of Ganymede, Europa orbits twice and Io orbits four times, this forces Io to have a more eccentric orbit. The eccentric orbit means that Io's orbital distance continuously varies, which causes expansion and contraction of its tidal bulge. This frictional energy is dissipated in the form of heat. Io’s internal heat melts the sulfur-rich core into liquid magma, which is contained in large subsurface chambers [3] . This process raises the internal pressure of Io and causes volcanic activity. It is believed that Io has a thin rigid lithosphere and a constant flowing liquid mantle due to its constant internal heating. It is estimated that the power dissipation from tidal interaction is two orders of magnitude greater than radioactive decay. For this reason, Io has a maximum observed temperature of ~1800K- the second highest in the solar system [3] . Another manifestation of the large power dissipation is a large heat flow, 30 times larger than found in Earth’s volcanoes.

Volcanic Features[ edit ] It is not surprising that Io’s surface is dominated by volcanic features. The surface is littered with pit craters, calderas (volcanic craters), lava flows, shield volcanoes, ash plains, sulfur (S) deposits and other features. Image of Active lava flows in the Tvashtar Paterae region. Images taken by Galileo in 1999 and 2000 There are over 500 volcanoes on the surface of Io. There are also over 200 calderas, some of which stretch up to 200km across; these calderas are surrounded by different patterns such as bright rings from condensing sulfur ejecta [2] . Volcanic eruptions cause these plumes of ejecta, which can be sprayed up to a height of 300km and 1000km in diameter [1] . The formation of the ejecta plumes is determined by the type of eruption and the characteristics of the material ejected (i.e. molecular composition or phase of matter). Large lava flows are common on the surface due to large volcanic plume velocities of ~1km/s.

Lava flows create intervent planes which are areas between volcanoes where lava flows are frequently resurfacing, keeping them flat [4] . Unlike the Earth, there has been no evidence shown that Io has plate tectonics; there are also anomalous isolated mountains in the polar regions [2] . Plasma Torus[ edit ] Recently, it has been discovered that Io has a plasma torus. The plasma torus is created by the volcanoes that eject sodium and sulfur gas and plasma into Io’s atmosphere. Since Io is not very massive it is not able to hold a substantial atmosphere, leaving behind a “tail” which follows Io’s orbit around Jupiter. Jupiter’s magnetic field strips off more than 1000kg of Io's material per second [5] . The plasma torus is held in place by Jupiter’s large magnetic field, which causes the charged particles (protons and electrons) in the field to orbit a center of rotation, which causes these particles to stay in a relatively small area. Some of these ions are drawn towards Jupiter’s atmosphere by its magnetic field lines, when these ions interact with Jupiter’s atmosphere, auroras are created.

The excess stripped ions in the torus double the size of Jupiter’s magnetosphere compared with theoretical calculations [5] . Spectral observations show that Io’s torus and ionosphere are depleted by processes that produce a large nebula expanding out to ~500 Jupiter radii [6] . One of the latest methods of studying the plasma torus is with high resolution (R~120000) spectra of neutral oxygen emissions (630nm) as well as other emissions with the Wisconsin H-Alpha Mapper (WHAM) instrument in Madison, Wisconsin. These observations have shown that emissions show significant long and short-term variations of oxygen emissions. Since intensity variations exist along with a long-term intensity average, it has been concluded that the emissions cause an interaction between Io’s torus and its atmosphere [7] . The reason for studying emissions is to measure the composition as well as velocity structures. This spectra is being taken with a dual Fabry-Perot etalon system to filter out the multiple orders that are produced by etalons [8] . Io's Surface and Subsurface[ edit ] Wikimedia Commons Io Interior Image Research is also being directed towards Io’s surface and subsurface processes.

Scientists are currently trying to map the anti-Jovian hemisphere as well as analyze volcanic, tectonic, and other processes affecting the region [9] . Observations show that Io’s entire surface is constantly changing because of subsurface processes, but most eruptions are found to be confined to isolated areas. Volcanic events only take place on about 17% of the surface which points back to the large lava flows that can extend up to 1000km [9] . Similar to Earth’s geysers, Io’s fissures release gases and liquids like sulfur vapor up to 225km and can last for days. Io’s surface has been found to be very active and volatile; it has been observed that changes in volcanic spray were detected in a 5.5 hour period. A New Frontiers class mission named Argus is a planned mission to send a spacecraft to Io that would orbit the moon 40 times at about 100km altitude. The goal of the mission is to attempt to answer basic questions about the possible habitation of planetary bodies like Europa and Enceladus, which are both under the influence of significant tidal heating [10] .

Europa[ edit ] Europa is the solar system's sixth largest moon. With a diameter of 3120 km, Europa is slightly smaller than Earth's moon, and is substantially larger than the dwarf planet Pluto. Europa has the smoothest and one of the youngest surface in the Solar System, Scientist think that Europa might have a liquid ocean under its icy crust and thus, scientist think it may harbor life. Europa was discovered in January 7 1610 by Galileo Galilei in 1610 at the same time that Io, Ganymede, and Callisto were found. The remaining 60 moons[ edit ] Jupiter has other remaining 60 moons (some may be captured Asteroids) are all far smaller than Ganymede, Callisto, Io and Europa even the fifth largest moon of Jupiter has a diameter under 200 km. The other moons names in order are in the Inner Group: (since Jupiter has a lot of moons they are divided into groups) Metis, Adrastea, Amathea and Thebe followed by the Themisto group with only one member which is Temistho.

The Himalia Group: Leda Himalia, Lysithea, and Elara. The Carpo Group which only member is the moon Carpo. An unamed group which only member is an unnamed moon (S\2003 J 12). Anake Group: Anake, Praxidike, Harpalyke, Iocaste, Euanthe, Thyone, Euporie , S/2003 J 3 , S/2003 J 18 , Thelxinoe , Helike , Orthosie , S/2003 J 16 , Hermippe , Mneme , S/2003 J 15 and S/2010 J 2.

The Carme Group: Herse , S/2003 J 10 , Pasithee , Chaldene , Arche , Isonoe , Erinome , Kale , Aitne , Taygete , S/2003 J 9 , Carme , S/2003 J 5 , S/2003 J S/2003 J 19, Kalyke , Eukelade and Kallichore. The Pasiphae Group: Eurydome , S/2003 J 23 , Hegemone , Pasiphaë , Sponde , Cyllene , Megaclite , S/2003 J 4 , Callirrhoe , Sinope , Autonoe , Aoede , Kore and S/2010 J 1 and the final group is another unnamed group with an only moon with a group all of its own (S\2003 J 2) Titan[ edit ] Titan is the second largest moon in the solar system; with a diameter of 5150 km, it is slightly smaller than Jupiter's Ganymede; it is larger than the planet Mercury.

Titan is the only planetary moon having a dense atmosphere. Titan's atmosphere is mostly composed of nitrogen with a trace of methane. Titan's Atmosphere is by far the densest of any satellite in the Solar System, being 50-60% denser than Earth's atmosphere. Other moons, if they have atmospheres (which the majority don't), have less than 1/1000 the pressure of Earth's atmosphere at sea level. The Atmosphere on Titan is dense enough for there to be rain; however, the rain is liquid methane. The temperature on Titan is so low (-333 degrees Fahrenheit) that methane is a liquid. Rhea[ edit ] Rhea is the second largest moon of Saturn and the ninth largest moon in the Solar System, with a diameter of 1528 km. The moon has a possible ring system. Rhea's low density of 1.23 suggests that it is composed of 75% water ice and 25% rock. Iapetus[ edit ] Iapetus is the third largest moon of Saturn and the 11th largest moon in the Solar System.

Iapetus holds the record for the Farthest Round Major moon of any Planet\Dwarf Planet being 93 times farther from Saturn than the Moon from the Earth. Iapetus diameter is 1472 miles (735 km). Half its surface is extremely bright while the other is extremely dark. Dione[ edit ] Dione is the second densest moon of Saturn (after Titan) at a density of 1.47 this means that it has more rocky material within than the other moons. Dione has a face which it's heavily cratered and another that it's almost completely clean of craters. At a diameter of 1122 km, Dione is the fourth largest moon of Saturn and the 15th largest in the Solar System Tethys[ edit ] Tethys is similar to Dione in many ways like size number of craters ext... .Tethys is the 16th largest moon of the Solar System and the 5th largest of Saturn.

Investigation and Research indicates that in the past, Tethys was a giant ball of liquid water that with the temperatures of the outer Solar System froze eventually Enceladus[ edit ] Enceladus is the 17 largest moon of the Solar System at 500 km across. Enceladus is the only Moon of the Solar System that shoots tons of water from its inside to outer space. Enceladus is much smaller than Titan, Rhea, Iapetu, Dione and Tethys but much bigger than Mimas, the Smallest round moon of Saturn. Mimas[ edit ] Mimas is the smallest round moon of Saturn and the 20th largest moon of the Solar System at a diameter of 396 km. Mimas has a huge crater being almost as half a big as Mimas itself which it would have been a little bigger and it would have destroyed Mimas. Hyperion and Phoebe[ edit ] Hyperion is the 8th largest moon of Saturn and 23rd in the Solar System. Hyperion is the only moon in the Solar System that rotates chaotically.

The density of Hyperion is one of the lowest in the Solar System at 0.5 grams per cubic centimetres which is lower than Saturn's which is 0.7 grams per cubic centimetre. Phoebe is the ninth largest moon of Saturn and one of the largest irregular moons in the Solar Sytem at a diameter of 220 km. Like Hyperion, Phoebe's rotation is not the same as its year, however Phoebe's rotation can be determined while Hyperions's cannot. Phoebe rotates once every eleven hours while its year is 550 days.

The Remaining 53 Moons[ edit ] The remaining 53 minor mons of Saturn are S/2009 S 1 ,Propeller moonlets ,Pan ,Daphnis ,Atlas ,Prometheus , ?(S/2004 S 6 · S/2004 S 4 · S/2004 S 3) ,Pandora Epimetheus ,Janus Aegaeon , (Telesto • Calypso) , (Helene • Polydeuces) Methone ,Anthe ,Pallene Kiviuq ,Ijiraq ,Paaliaq ,Siarnaq ,Tarqeq,Skathi , S/2007 S 2 , Skoll , S/2004 S 13 , Greip , Hyrrokkin , Mundilfari , Jarnsaxa , S/2006 S 1 , S/2004 S 17 , Narvi , Bergelmir , Aegir , Suttungr , S/2004 S 12 , Bestla , Farbauti , Hati , S/2004 S 7

 , Thrymr , S/2007 S 3 , Surtur, Fenrir , Ymir , Loge , Fornjot ,Albiorix , Bebhionn , Erriapus , Tarvos and Kari Uranus has 27 moons including Titania, Oberon,Umbriel and Ariel which are all over 1000 km Titania and Oberon[ edit ] Titania and Oberon are the largest moons of Uranus Titania being 1578 km in diameter make it also the 8th largest moon of the Solar System and Oberon the 10th largest moon of the Solar System at a diameter of 1522 km.

Both moons are heavily cratered like most moons. Both moons were dicovered by William Hershell on January 11 1787 Umbriel and Ariel[ edit ] Umbriel is the 13th largest moon of the Solar System at a diameter of 1168 Ariel is the 14th largest moon of the Solar System at a diameter of 1156 km. Both moons were discovered by William Lassell on October 24 1851 Miranda[ edit ] Miranda is the smallest round moon of Uranus and the 18th largest moon in the Solar System. Miranda is an icy moon which it is mostly composed of water ice and a small percent of rock. This moon was dicovered in February 15 1948 by Gerard P. Kuiper.

The Remaining 22 moons[ edit ] The other moons of Uranus are Cordelia , Ophelia · Bianca , Cressida , Desdemona , Juliet , Portia , Rosalind , Cupid , Belinda , Perdita , Puck , Mab,Francisco , Caliban , Stephano , Trinculo , Sycorax , Margaret , Prospero , Setebos and Ferdinand Triton[ edit ] Triton is the seventh largest moon in the solar system; its diameter of 2705 km is about 10% larger than the Dwarf Planet Pluto. Scientists believe that this moon is really an object that has been captured by Neptune's gravity. Triton is one of the coldest bodies in the Solar System being even colder than Pluto at -393 degrees Fahrenheit. In 360,000,000 years it is expected to pass the Neptune roche limit and disintegrate to form a planetary ring system Nereid[ edit ] Nereid is the third largest moon of Neptune at 170 km in Diameter.

Nereid is also one of the few moons in the Solar System that its year is not the same as its rotation Proteus[ edit ] Proteus is the largest irregular moon of the Solar System and the second largest moon of neptune and the 19th largest moon of the Solar System being 420 km in Diameter. The Remaining 10 Moons[ edit ] The other 10 moons are Naiad , Thalassa , Despina , Galatea , Larissa Halimede , Sao , Laomedeia , Psamathe and Neso Iapetus (Moon) Facts Iapetus Diagrams Iapetus size compared to the Moon and Earth Saturn’s moons size comparison (Pandora, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus and Phoebe) Facts about Iapetus Iapetus comes from the name of a Greek Titan, following along in the tradition of calling Saturn’s moons after the Titans. Iapetus has a bright and a dark hemisphere, with a ridge running along its equator. The dark region is called Cassini Regio and is the principal feature of the leading hemisphere.

The surface of Iapetus is heavily cratered, with large impact basins up to 580 kilometres across. Surface darkening on Iapetus comes from organic materials left behind as ice in the warmer Cassini Region region sublimates. The dark patches seem to be made of organic materials similar to those found in early meteorites or comets. There is also a suggestion that some material may have come from outside Iapetus. Iapetus’s equatorial ridge runs along 1,300 kilometres through the central region of the moon. It is about 20 kilometres wide and towers up 13 kilometres over the surrounding surface. No one is quite sure why or how it formed. The Voyager and Cassini missions have led in the exploration of Iapetus. Cassini has been able to study it over longer periods of time. Iapetus’s orbit is inclined to the plane of Saturn and is also quite far away. This makes it the only large moon from which an observer could see the rings. There currently no missions planned to explore Iapetus in the near future.

Sources: Iapetus: Saturn's Yin-Yang Moon Iapetus: Saturn's Yin-Yang Moon By Nola Taylor Redd, Space.com Contributor | June 27, 2016 04:22pm ET MORE These two global images of Iapetus show the extreme brightness dichotomy on the surface of this peculiar Saturnian moon. The left-hand panel shows the moon's leading hemisphere and the right-hand panel shows the moon's trailing side. Image published Dec. 10, 2009. Credit: NASA/JPL/Space Science Institute The light and dark faces of Saturn's moon Iapetus create a contrast that helped to hide the satellite for years, despite its distant orbit. The moon, which keeps the same face perpetually turned toward Saturn, remained shrouded in shadows, with its bright side only visible from Earth when it traveled on the west side of its primary. Discovery and naming Iapetus is one of four moons discovered by Giovanni Cassini in 1672. But the icy moon challenged the Italian astronomer.

He first spotted it on the west side of the planet, but when he attempted to observe it 39 days later on the eastern side, no trace of the satellite could be found. The pattern repeated itself over the course of the moon's 79-day orbit, leading Cassini to surmise that the moon was tidally locked, with one face darker than the other. Cassini named the four moons that he discovered (Iapetus, Rhea , Dione , and Tethys) the Sidera Lodoicea, or the Stars of Louis, after King Louis XIV. For years, the moons were referred to numerically, based on their distance from Saturn. Distant Iapetus started out as Saturn V, but the discovery of Mimas , Enceladus , and Hyperion bumped it down to Saturn VIII. Nearly 200 years later, John Herschel suggested that the moons around the ringed planet be named for the Titans, the siblings of the Greek god Cronus, who was Saturn to the Romans. In Greek mythology, Iapetus is a son of Uranus and Gaia and the father to Atlas and Prometheus.

His relationship to Prometheus, the Titan who gave fire to humans, led early Greeks to regard Iapetus as the father of the human race. Features on Iapetus take their names from the French epic poem "The Song of Roland." Composition and orbit Iapetus has a low density of only 1.083 grams per cubic centimeter, just a little more than liquid water, implying that it composed primarily of water, with rock making up less than a quarter of its composition. The walnut-shaped moon is not spherical, but has a bulging equator with squashed poles. The squashed shape of the moon resembles a satellite that rotates once every 10 hours, rather than the 79 days it takes Iapetus to make a full revolution. The angular structure of the moon has led to conspiracy-like suggestions that it is not a natural satellite but could have been built or modified by another civilization. However, its odd shape could easily have a natural explanation. Early in its life, when the moon still spun rapidly, a thick crust could have frozen the moon into its odd shape. Over time, the satellite's spin would have slowed until it eventually became tidally locked.

Iapetus is the third-largest moon orbiting Saturn, with a diameter of 914 miles (1,471.2 km). Although its radius is about two-fifths that of Earth's moon, its icy composition means that it is only about 2 percent as massive. The equatorial ridge of Iapetus can reach heights of up to 12 miles (20 km). This image reveals mountains only about half that height. Credit: NASA/JPL/Space Science Institute A chain of high mountains circle the equator , stretching more than halfway around the moon, though in it may have encircled it completely long ago. The ridge stretches more than 800 miles (1,300 km) around the moon's 2,871-mile (4,621 km) equatorial circumference. Some of the peaks reach heights exceeding 12 miles (20 km), making them among the highest mountains in the solar system. A line of white dots making up the ridge, informally called the Voyager Mountains, was first spotted and studied in the early 1980s by the spacecraft of the same name. Years later, NASA's Cassini probe studied the ridge in depth.

The white dots spotted by Voyager were not peaks but regions of ice on their eastern sides. The other mountains are covered with dark material. The Voyager Mountains reach as high as 6 miles (10 kilometers). The ridge wrapped around Iapetus' equator may have formed early in its history, when the moon spun faster than it does today. It may also have been created from material deposited by a ring or moon that collapsed onto the satellite. Iapetus travels around Saturn at a distance of 2,213,000 miles (13,561,300 km) from Saturn, the most distant of its major satellites. Unlike other, closer moons, Iapetus suffers very little tidal heating from the massive planet. As a result, the skin of the satellite does not show signs of melting and resurfacing that may have smoothed the outer layer of other moons. There are, however, other signs of change on its surface. In 2012, scientists announced they had detected landslides of up to 50 miles . These were likely generated when material fell from a great height and travelled a long way in the light gravity of the moon.

Given that Iapetus does have a high peak and the longest landslides were associated with the ridge (and related features), it's likely this would have been the cause. Scientists are hoping to learn more about this feature to better explain similar events on Earth and Mars. Both hemispheres contain a number of impact craters of varying sizes. The largest, Turgis, has a diameter of about 360 miles (580 km). Cassini captures its first detailed lok at the Voyager Mountains, first identified 25 years earlier. The mountains straddle the equator of the moon, with the region pictured morphing from the light to the dark section. Credit: NASA/JPL/Space Science Institute The dark side of the moon The most striking feature of Iapetus is its contrasting coloration . The leading hemisphere of the satellite is coal-black, while its backside is far brighter. As Cassini noticed, when the moon is facing Earth, its dark leading side helps to keep it hidden. The coal black region is called Cassini Regio, in honor of the Italian astronomer. A number of theories seek to explain the strangely contrasting satellite.

Particles from the smaller but more distant moon, Phoebe, may fall on the surface of Iapetus, constantly renewing the dark side. Eruptions of dark hydrocarbons from ice volcanoes could also explain the differentiation. Evidence for that theory came in 2009. Scientists detected a ring of material surrounding Saturn that likely came from Phoebe. By 2015, infrared observations from NASA's WISE spacecraft showed the Phoebe ring was a lot larger than previously expected . Its distance ranges from 100 to 270 times the radius of Saturn, or about 3.75 million to 10.1 million miles (6 million to 16.2 million km) from the planet. Thermal observations of the moon taken by the Cassini mission provide the best insight into the unique process. The slow rotation of the moon means that the dark surfaces, which absorb more heat than their icy counterparts, have more time to warm. Any icy material mixed with the dark surfaces is reduced to gaseous form, falling back on the cooler regions of the moon. The dark side then continues to grow darker, while the bright side grows brighter.

The process could have started long ago, with only a small amount of dark material to fuel it. As the material separated, the dark patch could have grown steadily over time, resulting in the yin-yang moon seen today. Scientists are not only looking at Iapetus and modeling it to explain the theory, but they have also tried comparing it to microwave emissions tracked on Earth . The key limitation is that ice on Earth melts into liquid water, so the team acknowledged that more study on this matter was required. Other locations that could serve as a point of comparison include the moons of Jupiter and the small, icy bodies of the Kuiper Belt beyond Neptune. Temperatures on the warmer dark side reach minus 143 degrees C (minus 226 F). The bright side, which absorbs less heat, is cooler, with temperatures averaging minus 173 C (minus 280 F).

Quick facts Average orbital distance: 2,212,610 miles (3,560,851 km) Closest approach: 2,147,780 miles (3,456,518 km) Farthest approach: 2,277,440 miles (3,665,184 km) Orbit eccentricity: 0.0293 Rhea, moon of Saturn - The Solar System on Sea and Sky Cassini image of Rhea showing light colored ice fractures (NASA/JPL/Space Science Institute) Wife of Chronus Rhea [REE-a] is the fourteenth of Saturn's known moons and is the second largest. It is the largest airless moon in the Saturnian system. Rhea was named after the sister and wife of Chronus in Greek mythology (Saturn in Roman). She was also the mother of Demeter, Hades (Pluto), Hera, Hestia, Poseidon (Neptune), and Zeus (Jupiter). Rhea was discovered by Giovanni Cassini in 1672. Nearly everything we now know about Rhea was discovered during the two Voyager missions.

Cassini close-up image of Rhea showing numerous craters (NASA/JPL/Space Science Institute) Voyager 1 close-up photo of Rhea's north polar region (NASA/JPL) Another Icy World Rhea is an icy body very similar to Dione, although slightly larger in size. It has a very low density, which indicates that it is composed mainly of water ice with rocky material making up less than one third of its total mass. The temperature on Rhea ranges from -281° F (-174° C) in the sunlight to -364° F (-220° C in the shade. The icy moon Rhea is seen in orbit above the cloud tops of Saturn in this Cassini spacecraft image. Rhea is Saturn's second largest moon with a diameter of 950 miles (1,529 kilometers) (NASA/JPL) Features of Rhea Rhea is one of the most heavily cratered satellites in the Solar System. The surface features of this moon can be divided into two different geological areas based on the density of the craters. The first area contains craters that are larger than 25 miles (40 km) in diameter.

The largest of these craters is Izanagi. It has a diameter of 140 miles (225 km). Craters in the second area are smaller than 25 miles in diameter. The difference in these areas indicates that some great event served to resurface parts of this moon at some point in the past. Similar differences in crater size can be found on Mimas and Dione. Like Jupiter's moon Callisto, Rhea's craters lack the high surface features found in craters on Mercury and the Moon. Like Dione, Rhea's orbit around Saturn is synchronous, meaning that it always keeps the same face toward Saturn. On the trailing hemisphere of Rhea can be found several bright, wispy lines. These linear features are believed to be fractures, and may indicate that Rhea has expanded and contracted due to internal heating and cooling. Similar linear features are found on Dione. Rhea has no detectable atmosphere.

Question: Rhea and Iapetus are the second and third largest moons of which planet?
Answer: SATURN